Storage display tube with a shield separator between the writing gun and the flood gun



Oct. 1l, 1966 P. E. CARNAHAN ETAL 3,278,780

STORAGE DISPLAY TUBE WITH A SHIELD SEPARATOR BETWEEN THE WRITING GUN ANDTHE FLOOD GUN Filed Feb. 21. 196s Paul E. Carnahan d and Eric A.Ziemer,Jr

ATTORNEY States This invention relates to storage tubes and moreparticularly to improvements in the electron gun assembly within thestorage device.

Direct view storage cathode ray tubes for storing information normallyin the form of a charge image on a storage mesh and then providingdirect viewing of the image on a phosphor screen are well known in theart. The tubes generally contain, in `addition to a conventional outputphosphor screen and a writing gun similar to those used in aconventional cathode ray display tube, a storage mesh on whichinformation is written by means of a writing gun. The information isthen viewed on the phosphor screen by means of directing a large areaooding or viewing electron beam through the apertures in the storagegrid mesh. The writing operation is performed in these tubes by aconventional type of electron gun. The gun is provided withelectrostatic focusing and deiiection. The electron gun is capable ofiforming a well-defined beam of high current density to provide goodresolution at high writing speeds. In general, at least two writing gunsare provided within the same envelope and it is customary to provideelectrostatic deflection for the writing beams. The writing guns arenormally positioned off the longitudinal axis of the tube and at aslight angle thereto. A viewing electron gun which provides a broad beamof electrons is normally located be tween the two write guns and locatedsubstantially on the longitudinal axis of the tube.

lt has been found in this type of tube that nonuniformity in thedeiiection of the writing beam gun is a serious problem. This problemhas been found to be primarily due to feedback of electrons from the oodor viewing gun section to the writing gun deflection plates.

Accordingly, the general object of this invention is to provide a newand improved storage tube in which the writing `gun is substantiallyisolated from electron feedback from the viewing gun.

it is another object to provide an improved electron gun assembly for astorage tube.

It is another object to provide a new and improved electron gun assemblyfor use in a storage tube which is simple, rugged and inexpensive tomanufacture.

Briefly, this invention accomplishes the above objects by providing anelectron gun assembly including a structure or grid positioned in frontof the writing gun to provide isolation, with suitable potential, of thedeiiection electrodes of the writing gun from feedback of electrons fromthe viewing gun to the deiiection electrodes of the write gun.

Further objects and advantages of the invention will become apparent asthe following description proceeds and features of novelty whichcharacterize the invention will be pointed out in particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to theaccompanying drawings, in which:

FIGURE 1 is a schematic showing, partially in section, of a cathode raystorage tube in accordance with the present invention;

FlGURE 2 is a sectional View taken along the line lI-II of FIGURE 1;

atent ice FIGURE 3 is a sectional view taken along the line III-III ofFIGURE 2.

Referring in detail to FIGURE 1, a direct view storage tube isillustrated and includes an evacuated envelope 10. Positioned at one endof envelope is a face plate 12 on which is deposited a layer 14 ofphosphor material capable of emission of light in response to electronbombardment. Positioned adjacent to the phosphor screen 14, there isprovided a storage grid which consists essentially of an electroformedmesh 22 of an electrically conductive material such as nickel with acoating 24 of a suitable dielectric such as magnesium oxide on theopposite side V`ofn the mesh 22 with respect to the phosphor screen 14.A collector electrode 26 in the form of a mesh is disposed adjacent tothe storage grid 20. The tube base 16 is positioned at the opposite endof the envelope 10 with respect to face plate 12. Lead-in members 18 forproviding support and suitable voltages to the electrodes within thetube are provided through the tube base 16. Mounted to the tube base 16by means of the lead-in members 18 is the electron gun assembly 30 whichconsists of two writing guns 40 and a flood gun 60. The two writing gunsare identical in design and are each `capable of forming a wvell-denedbeam having high current density with suitable focusing and accelerationso as to direct a pencil type electron beam onto the storage grid 20.Each of the electron guns 40 consist of an indirectly heated cathode 42,a control grid or first grid 44, a rst and second anode 46 and 49 whichare the second and fourth grids and which are internally connected and afocusing grid 4S which is the third grid. Also included within theelectron gun assembly are horizontal and vertical deflection plates 51,52, 53 and 54 for deflecting the electron beam to scan a raster over thestorage mesh 20 in response to suitable deflection voltages applied tothe deflection plates. The electron guns 4t) are formed into a unitarystructure by providing stud members from the electrodes which areembedded in suitable insulating rods as is well-known in the art. Thetwo write guns 40 are positioned off of the axis of the electron tubeand directed to provide electron beams which converge substantially atthe storage mesh 20.

Positioned between the two write guns is a viewing gun which consists ofa cathode 62, a control grid 64 and an accelerating grid assembly 65.The portion of the accelerating grid structure 65 which performs theaccelerating action for the viewing gun consists of a plate member 66transverse to the longitudinal axis of the tube and having an aperture77 therein. Spacer contact members 78 are provided on the outerperiphery of the member 65 to position the electron gun assembly withinthe neck of the envelope 10 and in addition making electrical contact toa conductive coating 68 on the inner surface of the envelope. Theconductive coating 68 is at the same potential as the member 66 and formtogether the second grid of the flood gun 6). Another conductive coating69 is provided on the inner wall of the envelope spaced from the coating68 and between the coating 68 and the storage mesh 20 and may bereferred to as the third grid of the iiood gun and is also sometimesreferred to as a collimating electrode.

Referring now in detail to FIGS. 2 and 3, the transverse plate 66 is aflat disc of a suitable material such as stainless steel havingappropriate rectangular openings 70 and 72 to allow for the ow ofelectrons from the two write guns 40. In addition, the centrally locatedaperture 77 provided in plate 66 provides focusing operation for theviewing gun 60. The portion of the plate 66 surrounding the aperture 77is positioned adjacent the apertured end of the grid electrode 64 of theviewing gun a 60. Positioned to the rear of the plate 66 with respect tothe viewing screen 14 is an electrode '79 of annular configurationhaving an outer diameter less than the outer diameter of the plate 66.The inner diameter of the member 79 is such as to provide clearance withrespect to the outer diameter of the grid 64 of the viewing gun 60. Theinner portion of the electrode 79 is a mesh 73. It is only necessarythat the mesh portion 73 of the electrode 79 be of substantially thesame area as the rectangular openings 70 and 72 in the plate 66 so thatthe outer edge of the mesh portion 73 does not interfere with theelectron beams from the writing guns 40. The mesh 73 may be mounteddirectly to the annular member 79 by using a thin welding strip or astamped part. Another possible method would be to mount the mesh 73between two similar stamped parts and in turn Weld the complete meshassembly to the member 79. The member 79 is mounted to the back side ofthe plate 66 by ceramic separators 80. In the specific embodiment shown,there are four ceramic separators 80 positioned about the periphery ofthe electrodes. This type of spacer is more fully described in thecopending application Serial No. 166,047, filed January l5, 1962,entitled, Direct Viewing Storage Tubes Having Ceramic Spacers BetweenCollector Electrode and Storage Grid, by E. Ziemer et al. and assignedto the same assignee as this invention, and which is now U.S. P-atent3,160,773, granted December 8, 1964. The ceramic tab assembly includesceramic blocks 81, preferably cylindrical in shape, the ends of whichare provided with a metallic coating of a few thousandths of an inch ofmolybdenum manganese. This coating is applied by painting the surface ofthe ceramic blocks. The ceramic blocks 8l are porous so that the coatingpenetrates the block to provide a roughened surface which is interlockedwith the interstices of the ceramic block. To these coatings on theopposite ends of the ceramic blocks, there is brazed tabs .82 of asuitable material such as a copper silver eutectic lalloy. This type oftab constitutes a convenient means of attaching the two electrodes 66and 79 by brazing or welding. The ceramic tab assemblies 8f) may beassembled and then the two electrodes 66 and 79 and the yceramic tabs 80assembled to provide the structure.

In addition, a plate 74 having an enlarged aperture 86 may be providedto the rear of the mesh member 69 at a distance of approximately .100inch and provided with la flange 76 about its outer periphery such thatthe outer periphery is of substantially the same diameter as the platemember 66. The two members 66 and 74 may be physically and electricallyconnected together by means of three or four metal straps 67 of asuitable material such as stainless steel which are welded to the twoelectrodes 66 and 74. The straps 67 also provide electrical connectionbetween the electrodes 66 and 74. The bulb spacers '78 may be secured toeither one of the two plate members 66 or 74 and provide the function aspreviously pointed out.

In the operation of the device, the problem of feedback of electronsgenerated by the flood gun 60 onto the deflection plates 51, 52, 53 and54 normally arises when yan erase pulse is applied to the storageelectrode 20. The result is that the low velocity electrons generated bythe viewing gun 60 are returned back towards the electron gun assembly30 and look for the most positive potential electrode. The collectingelectrode 26 normally operates at a potential of 250 volts positive withrespect to ground. The electrode 69 is at about 75 volts positive whileelectrodes 66, 68 and 79 are at a positive potential of about 100 volts.The deflection electrodes 51, 52, 53, and S4 are normally at the samepotential as the electrodes 66, 68 and 79 which in this case is 100volts. However, in the application of deflection signals to thedeflection plates 51, 52, 53 and 54, one of the deflection plates mayrise in potential to `about 300 volts positive with respect to ground.This results in this deflection plate being the most positive electrodethat the electrons can see and the electrons will be collected by thedeflection plate. This in the prior art type of device modifies thedeflection voltage applied to the deflection plates and results innonuniformity of deflection.

By providing the structure as herein described in which the electrode 66is at a potential of about 100 volts positive with respect to ground andwith the mesh electrode 79 insulated from the electrode 66 and connectedto the potential of the first grid 64 of the flood gun 66, normally fromzero to negative 50 volts with respect to ground, the electrons areunable to see the high positive potential on the deflection plates 51,52, 53 and 54 and will be collected by the electrode 66 which of courseresults in no operational disadvantage to the system. It is found thatthe mesh electrode 79 must be operated at a negative potential withrespect to the electrode 66 to perform its function eflectively.V It istrue that even a mesh operating at the same potential as 66 wouldintercept some of the electrons fed back to the deflection plates, but amuch more effective reduction is provided by applying a negative voltageto the mesh electrode 79. It is found that the potential on electrode 79has no detrimental effect on the writing gun electron beam. In addition,by providing a negative voltage on the mesh electrode 79 with respect toelectrode 66, it is obvious that this permits the use of a hightransmission mesh of about percent and the writing beam current is notappreciably reduced as it passes through this mesh area. It is found inthose tubes in which the mesh was not utilized that the magnitude of thefeedback current to the deflection plate was about 20 microamperes. Byutilization of the mesh electrodes, it is found that for all practicalpurposes the feedback current was completely eliminated.

The resulting structure while providing the essential electricalcharacteristics important in preventing the electron feedback to thedeflection plates of the writing guns also provides a rugged assembly.The resulting construction of the assembly is simple to fabricate andreproduce.

While there have been shown and described what are at present consideredto be the preferred embodiments of the invention, modifications theretowill readily occur to those skilled in the art. It is not desired,therefore, that the invention be limited to the specific arrangementshown and described and it is intended to cover in the appended claimsall such modifications as fall within the true spirit and scope of theinvention.

`Ve claim as our invention:

1. A storage tube comprising an envelope and including a storage targettherein, an electron gun assembly disposed at the opposite end of saidenvelope with respect to said storage target, said electron gun assemblycomprising at least a write gun and a flood gun, said write gunincluding a plurality of deflection electrodes, a member transverse tothe longitudinal axis of said tube and positioned between said electronguns and said storage target and mechanically assembled to said electrongun assembly, said transverse member including a first opening throughwhich the electrons from said write gun are directed toward said storagetarget and a second opening smaller than said first opening centrallylocated in said transverse member through iwhich the flood electron beamelectrons leave said electron gun assembly and are directed onto saidstorage target, a mesh electrode provide-d between said second aperturein said transverse member and the deflection plates of said write gun toprevent electrons from said flood gun being collected on said deflectionplates.

2. A storage display device comprising an envelope and including thereina storage target, an electrode assembly including -at least a writingelectron gun and a viewing electron gun positioned at the opposite end`of the envelope with respect to said storage target, said writingelectron gun including a plurality of deflection plates, said electrodeassembly secured to the base of said envelope at one end and positionedwithin said envelope by means of spacer members provided at the otherend of said electrode systems Iand on the periphery of a transversemember of said electrode system, said transverse member including a rstaperture through which the writing electron beam is directed onto saidstorage target, .said transverse member also including a second aperturethrough which said viewing electron beam is directed onto said target, aconductive mesh electrode within said electrode assembly positionedbetween the detlection electrodes of said writing electron gun and saidstorage target to prevent collection of electrons from said viewingelectron gun on the deilection plates of said writing electron gun.

3. A storage display tube comprising an envelope, a phosphor displayscreen provided at one end of said envelope, a storage mesh positionedadjacent to said phosphor display screen, an electron gun assemblyprovided at the opposite end of said envelope with respect to saiddisplay screen and including at least a writing electron gun havingvertical and horizontal deflection plates and a flood gun, a transversemesh provided within said electron gun assembly between said deflectionplates of said Iwriting electron gun and said display screen7 saidtransverse mesh operating at a negative potential with respect to saiddeflection plates of said writing electron gun to prevent collection ofelectrons from said ooding gun on said deflection plates.

4. A storage display tube comprising an envelope, a phosphor displayscreen provided at one end of said envelope, a storage mesh positionedadjacent to said phosphor display screen, an electron gun assemblyprovided at the opposite end of said envelope with respect to saidstorage mesh and including at least a writing electron gun havingvertical and horizontal deection plates, a transverse diaphragm providedat the end of said electron gun assembly and between the deflectionplates of said writing electron gun and said display screen, saidtransverse diaphragm having a large aperture to provide passage ofelectrons from said writing gun to said storage mesh, a viewing electrongun centrally disposed Within said electron gun assembly with a smallaperture provided in said transverse diaphragm for focusing theelectrons emitted from said viewing gun, said transverse diaphragmoperating at a positive potential with respect to the cathode of saidviewing gun, a mesh electrode positloned between said transverse memberand the dellection plates of said writing electron gun and insulatedtherefrom and operating at a negative potential with respect to thedeflection plates of said writing electron gun and said transversediaphragm.

5. A direct viewing storage tube comprising an envelope, a storagescreen, a `phosphor display screen and an electron gun assemblyincluding a plurality of electron guns disposed at the opposite end ofsaid envelope with respect to said display screen, said electron gunassembly comprising at least a high velocity electron gun and a lowvelocity electron gun, said high velocity gun including deflectionelectrodes, a transverse member positioned between said electron gunsand said display screen and mechanically assembled to said electron gunassembly, said transverse diaphragm including a large opening throughwhich high velocity electrons from said high velocity gun are directedonto said screen and a small opening through which the lowvelocityelectron from said low velocity gun leave such assembly and aredirected onto said storage screen, a mesh electrode provided betweensaid large aperture of said transverse diaphragm and the detiectionelectrodes of said high velocity gun and operating at a negativepotential with respect to the potential applied to sai-d transversediaphragm to prevent low velocity electrons from being collected on saiddeflection electrodes.

References Cited by the Examiner UNITED STATES PATENTS 3,131,324 4/1964Madden et al 313-82 JAMES W. LAWRENCE, Primary Examiner.

V. LAFRANCHI, Assistant Examiner.

1. A STORAGE TUBE COMPRISING AN ENVELOPE AND INCLUDING A STORAGE TARGETTHEREIN, AN ELECTRON GUN ASSEMBLY DISPOSED AT THE OPPOSITE END OF SAIDENVELOPE WITH RESPECT TO SAID STORAGE TARGET, SAID ELECTRON GUN ASSEMBLYCOMPRISING AT LEAT A WRITE GUN AND A FLOOD GUN, SAID WRITE GUN INCLUDINGA PLURALITY OF DEFLECTION ELECTRODES, A MEMBER TRANSVERSE TO THELONGITUDINAL AXIS OF SAID TUBE AND POSITIONED BETWEEN SAID ELECTRON GUNSAND SAID STORAGE TARGET AND MECHANICALLY ASSEMBLED TO SAID ELECTRON GUNASSEMBLY, SAID TRANSVERSE MEMBER INCLUDING A FIRST OPENING THROUGH WHICHTHE ELECTRONS FROM SAID WRITE GUN ARE DIRECTED TOWARD SAID STORAGETARGET AND A SECOND OPENING SMALLER THAN SAID FIRST OPENING CENTRALLYLOCATED IN SAID TRANSVERSE MEMBER THROUGH WHICH THE FLOOD ELECTRON BEAMELECTRONS LEAVE SAID ELECTRON GUN ASSEMBLY AND ARE DIRECTED ONTO SAIDSTORAGE TARGET, A MESH ELECTRODE PROVIDED BETWEEN SAID SECOND APERTUREIN SAID TRANSVERSE MEMBER AND THE DEFLECTION PLATES OF SAID WRITE GUN TOPREVENT ELECTRONS FROM SAID FLOOD GUN BEING COLLECTED ON SAID DEFLECTIONPLATES.